Re: [Boost-bugs] [Boost C++ Libraries] #8554: make_variant_over requires Extensible Sequence

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #8554: make_variant_over requires Extensible Sequence
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-05-08 01:19:48

#8554: make_variant_over requires Extensible Sequence
----------------------------------------------------+-----------------------
  Reporter:  Darryl Green <darryl.green@…>          |       Owner:  ebf    
      Type:  Bugs                                   |      Status:  new    
 Milestone:  To Be Determined                       |   Component:  variant
   Version:  Boost 1.53.0                           |    Severity:  Problem
Resolution:                                         |    Keywords:         
----------------------------------------------------+-----------------------

Comment (by Darryl Green <darryl.green@…>):

 Sorry about formatting - try this....

 {{{#!C++
 // possible "fix" to apply in make_variant_over
 typedef boost::mpl::vector<> empty; typedef
 boost::mpl::insert_range<empty, boost::mpl::end<empty>::type,
 Sequence>::type ExtensibleSequence;

 // example
 #include <string>
 #include <boost/variant.hpp>
 #include <boost/mpl/joint_view.hpp>
 #include <boost/mpl/insert_range.hpp>


 typedef boost::variant<int> v1;
 typedef boost::variant<std::string> v2;
 typedef boost::make_variant_over<boost::mpl::joint_view<v1::types,
 v2::types>::type>::type v3; // FAILS - requires Extensible Sequence
 //typedef boost::variant<int, std::string> v3; // OK (obviously)
 //typedef boost::make_variant_over<boost::mpl::insert_range<v1::types,
 //boost::mpl::end<v1::types>::type, v2::types::type>::type>::type v3; //
 OK (so types is probably an Extensible Sequence as insert_range works on
 it...)


 int main(int argc, char *argv[])
 {
         v1 a = 1;
         v2 b = "2";
         v3 c = a;
         return boost::get<int>(c);
 }
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/8554#comment:1>
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